This invention relates generally to a multilayer film, a meat product package comprising an enclosing multilayer film and an insitu aqueous medium-cooked meat product, i.e., the cook-in type, and a method for preparing a cooked meat product. In the method of the invention the meat is placed in a flexible tube formed of this film, hermetically sealed and insitu cooked by an aqueous medium. During the insitu cooking, the film inside surface is against the meat outer surface and develops a contiguous adhering relation therewith.
There are numerous requirements for a multilayer cook-in shrink film including: delamination resistance, low oxygen permeability, and high temperature strength. For certain end uses as for example packaging of chunked and formed meat products for cook-in, the film should provide heat shrinkability representing about 30-50% shrinkability at about 90.degree. C. Another very desirable characteristic for meat cook-in shrink films is adherence to the meat outer surface thereby preventing "cook-out", which is the collection of juices between the meat outer surface and film inner surface.
Probably the most commonly used inner layer in multilayer barrier-type shrink films is ethylene vinyl acetate. However, the prior art has recognized that ethylene vinyl acetate (EVA) does not provide good meat adhesion. For example, Judd et al U.S. Pat. No. 4,463,778 teaches that regenerated cellulose casings may be internally treated with vinyl acetate polymer to produce a coating which causes the casing to adhere to dry sausage emulsion and follow the sausage shrinkage during curing, but provide a low level of meat adhesion. In this manner the coating readily releases from the dried sausage emulsion when the casing is separated therefrom.
Because of the notoriously poor adhesion of ethylene vinyl acetate to meat, the prior art has employed various coatings or layers between an EVA substrate and the meat to provide good adhesion. Also, the prior art has developed a number of multilayer plastic cook-in films and certain of these are in commercial use. For example Bieler et al U.S. Pat. No. 4,104,404 describes a ten layer film comprising four central nylon layers, an ionomer layer on each outer side of the central layers, and two outer polyethylene layers on each outer side of the ionomer layers. The patentee demonstrates that delamination of the outer polyethylene layer under cook-in conditions was only avoided by irradiation dosage of the entire multilayer film at a level of at least 6 MR. This film does not appear to provide high meat adhesion.
Another commercially employed cook-in film is the type described in Oberle et al U.S. Pat. No. 4,469,742, comprising six layers irradiated to dosage of at least 6 MR. The central barrier layer is hydrolyzed ethylene-vinyl acetate copolymer (EVOH), chosen because of its higher softening point and superior oxygen barrier properties as compared to the saran-type barrier layer commonly used in multilayer films for ambient temperature applications. On each side of the barrier layer is an adhesive layer such as chemically modified polyethylene, eg. Plexar. On the outer side of each adhesive layer is a shrink layer such as ethylene-vinyl acetate copolymer (EVA), and the outside (abuse) layer is also the EVA type having a vinyl acetate content of about 5-12 wt.%. The innermost (heat sealing) layer may for example be a propylene-ethylene random copolymer (PER). If meat adhesion is required, an additional ionomer layer is used as the innermost layer.
One general concern in the extrusion manufacture of multilayer films containing EVOH is that the process conditions be such that gel formation is avoided. This may occur if resins are retained in the extruder passages and exposed to heat for prolonged periods so as to form oxidized particles which ultimately cause bubble breakage or appear in the finished film.
It will be apparent from the foregoing that these prior art cook-in films are complex both in terms of multiple materials and sophisticated manufacturing techniques i.e. six layers and relatively high irradiation dosage level to avoid delamination. Further, some of these films do not provide meat adhesion and an additional layer is needed for this specific purpose.
It should also be recognized that the ease of establishing and maintaining good adhesion between a cook-in film inside surface and the meat depends to some extent on the type of meat. For example, with most meats, including premium grade ham having less than about 10% fat and usually less than about 5% high collagen meat protein of the total available meat portion, it is less difficult to achieve good meat adhesion and little fat-out than with high fat content meats wherein the fat is in the suspended state. In particular, when the meat to be cooked insitu is a commodity style boiled ham having a product composition of more than about 10% fat and usually more than about 5% high collagen meat portion, it is much more difficult to obtain and maintain good meat adhesion.
One approach to this problem is to apply starch particles to the outer surface of the EVA inner layer of a multilayer film. This is preferably done by applying the starch particles to the hot EVA surface as an integral part of a coextrusion process forming the multilayer film. Alternatively, dispersion may be accomplished by dusting the starch particles on the cooled surface. The external starch particle-containing EVA surface is then irradiated. During insitu cooking, excellent adhesion develops with low fat and/or low collagen meats or other meats of the gel state fat type as for example fleishwurst. In ham, fat is in a state of suspension whereas in fleishwurst the fat is in the gel condition. The latter is much more stable and less prone to separate during cooking. This means that meat adhesion to the film inner surface is more readily developed during insitu cooking and maintained thereafter. The above-described external starch system has been quite successful in commercial use with low fat and/or low collagen as well as the gel state fat types of cook-in meats, but does not provide sufficient adhesion with the high fat/high collagen meats such as commodity style boiled hams.
Starch is currently supplied in concentrate form for inclusion in thermoplastic formulations to manufacture biodegradable plastics as for example in the form of films. By a combination of biological and chemical processes over a finite time period, these biodegradable films initially experience deterioration or loss of physical properties. These processes facilitate a breakdown of the primary molecular structure (i.e. the film polymer chains) ultimately rendering it to a state in which direct biological attack can occur. One such starch concentrate is Polygrade II 20835, manufactured by Ampacet Corporation, Mt. Vernon, N.Y. This starch concentrate comprises 60% linear low density polyethylene (LLDPE), 38% starch and 2% oxidation promoter, all by weight.
One object of this invention is to provide a flexible tube formed of multilayer film having less than six layers and with an inner layer providing improved adhering relation to high fat and/or high collagen type meat product of the suspended fat type during insitu cooking in an aqueous medium.
Another object of this invention is to provide a meat product package including an insitu aqueous medium-cooked high fat/high collagen meat product with its outer surface in adhering relation to the inner layer of a multilayer film having less than six layers and which satisfies the other requirements of a cook-in film.
A further object is to provide such a high fat/high collagen meat product package with a three layer film.
Still another object is to provide a method for preparing an insitu cooked high fat and/or high collagen meat product of the suspended fat type in a flexible tube having less than six layers, with improved adhering relation between the meat outer layer and film inner layer.